Lung disease in individuals, especially children, with HIV-1 infection is a major cause of morbidity and mortality. The principal targets for HIV-1 infection in the lung are CD4 cells of T lymphocyte and monocyte/macrophage lineages. Virus infection of CD4 lymphocytes produces constant and accelerated T cell death with devastating impact on T cell attrition and immunologic function. In contrast, HIV-1 infection of tissue macrophages does not immediately produce cell death, but may establish for the virus a shelter from the host immune system and a reservoir from which new viruses can be activated. The long term objective of the proposed research is to elucidate mechanisms involved in activation of HIV-1 in tissue macrophages. The hypothesis is that natural genetic variation of transcriptional regulatory elements in the long terminal repeat (LTR) sequences of the HIV-1 genome modulate activation and quiescence of the virus in macrophages by interaction with lung endothelial or fibroblast cells. The specific aims of the proposed research include: (1) to compare functional and genetic characteristics of virus LTRs from HIV-1 infected children with and without manifestations of pulmonary disease; (2) to measure the effectiveness of the promoter function of LTRs from viruses in lung versus peripheral blood from HIV-1 infected children with or without pulmonary disease; and (3) to identify LTR sequences that participate in mediating HIV-1 replication and activation in cells of the monocyte/macrophage lineage by in vivo footprinting using a novel strategy to distinguish between the 5' and 3' LTRs. The proposed interdisciplinary strategy focuses on viruses within lung tissues of infected children, implements novel in vitro methods to culture macrophages with lung-derived endothelial and fibroblast cells, and integrates data from clinical and research sources. The results will identify mechanisms by which cell contact between macrophages and lung endothelial or fibroblast cells modulates virus factors in the LTR and mediates virus activation.